Electric discharge tube



Aug. 16, 1949.

M. J. o. STRUTT ET AL I ELECTRIC DISCHARGE TUBE Filed April 18, 1946 FIG?) INVNTORS ATTORNEY Patented Aug. 16, 1949 i 2,478,986 ELECTRIC DISCHARGE runs Maximiliaan Julius Otto Strutt and Aldert vander Ziel, Eindhoven, Netherlands, assignors, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application April 18, 1946, Serial No. 662,969

- Inthe Netherlands May 27, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires May 27, 1961 In the endeavours which are being made'to construct discharge tubes so as to, make them suitable for amplifying or generating electric oscillations. of very high frequency and short waves a number of problems arise; many of these problems can be solved, by reducing the dimensions. of the tubes and of their various components and simplifying the circuits connected to the tubes. The use of these means eventually gives rise to the well-known tubes of small dimensions in which electrodes spaced a very small distance apart are connected to conductors which may constitute the circuits connected to the tube, use being made in this case of so-called Lecher lines. 7

An important problem in the construction of short-wave tubes and circuits, to which special attention has been given by the applicant, is the damping of. the input circuit by the resistance and capacity connected in parallel therewith and formed by the combination of cathode and the next following electrode. The space between the'cathode and the first grid, or between the cathode and the anode in the 'case of a diode, may be assumed to be built up from a condenser between the first grid or the anode and that side of the emitting layer of the cathode which is adjacent thereto and in series therewith a condenser and a resistance formed by the emitting layer itself; as will be established hereinafter, the properties of this layer may play an important part in a tube for short-wave purposes. Y

In general the opinion was held that improving results in the use of discharge tubes for short and very short waves could be attained by decreasing and decreasing the electrode spacings; researches by the applicant, however, revealed that this is not sulficient, that even in some cases disadvantages may accrue when reducing and reducing the distance from cathode to grid, or with a diode the distance from cathode to anode, without considering the emitting layer of the cathode. The researches underlying the invention revealed that it is not so much the distance from cathode to the next following electrode which should be small but that provision should be made that the ratio of the thickness of the emitting layer to the distance of the external surface of this layer from the next following electrode should be a minimum. It follows that it is not sufficient to reduce the distance of the cathode from the next following electrode but that the thickness of the emitting layer should also be a minimum. Th discharge tube according to the invention and its component members 4 Claims. (Cl. 250-27.5)

are proportioned insuch manner that the dis- 7 microns.

tance of the external surface of the, emitting layer of the cathode from the next following electrode is less than 0.5 mm. and the ratio of the thickness of the emitting layer to the distance just mentioned is less than 0.1. It follows that the maximum thickness of the emitting layer is 50 microns. It is, however, preferable that this thickness should be further reduced and should be less than 25 microns, very good results being attained in the use of the tubes on short wave when this thickness is less than 10 microns. The calculations and researches undertaken by the applicant show that for very short waves, that is to say decimetre and centimetre waves, the best results can only be attained if not only the distance from cathode to the next following electrode but also the thickness of the emitting layer itself are rendered a minimum, it being generally preferable for the distance of the cathode from the next following electrode to be reduced as far as possible. In connection with the use of very short waves, distances for example less than 0.25 mm. and less than 0.1 mm. are favourable.

It'is quite true that in the literature it has been suggested that for certain reasons the emitting layer of the cathode should be chosen so as to be thin, for example thinner than or even- 50 In practice the use of such thin layers entails difliculty, particularly in manufacture, so that the use of such thin layers is very reluctantly resorted to. Researches undertaken by the applicant on the subject revealed that if tubes are to be made suitable for amplifying or generating electric oscillations of decimetre and centimetre waves it is necessary to resort to such thin layers and that it is even necessary to choose very thin emission layers, even if, for example in manufacture, certain difficulties would accrue. Obviously, it is necessary to take care that the emitting layer is applied in such a manner that a very uniform layer is obtained; for this purpose the application is preferabl effected by an electrolytic or cataphoretic process or again by vaporation.

The importance of the ratio of the thickness of the emitting layer to the spacing between the external surface of this layer and the next following electrode may be seen as follows:

As described hereinbefore it is possible to aasume the combination of the cathode and the next following electrode to be constituted by a capacity (C1) between the external side of the emitting layer and the next following electrode, and by a capacity (C2) and a resistance (R2) formed by the emittin layer itself, as indicated by the equivalent circuit of Fig. 3.

Now, if w=21rf in which I is the frequency, the equation w (Cl+C2) .R2 1 is generally satisfied so that the capacities and resistance here mentioned may be assumed to be replaced by the capacity C1 and the resistance R2 connected in series therewith. This is a condenser having a loss angle 6 which angle is the complement of the power factor angle, such that tan 6:wC1R2 (1) 1 mZQo If A is the surface area of the cathode, d the thickness of the emitting layer, R the specific resistance of this layer and a the distance of the layers external surface from the next following electrode.

these values substituted in (3) yield Here, :1, a and A are in ems.

It is thus apparent that among other things a small ratio d/a is important. If this ratio equal to or less than 0.10 the tube is suitable for use for wavelengths less than 1 metre.

In order that the invention may be clearly understood and readily carried into eifect it will now be described more fully with reference to the accompanying drawings in which,

Figure 1 is a horizontal sectional view of a triode structure;

Figure 2 is a schematic view of the cathode and grid elements to show the dimensional relationships, and

Figure 3 is an equivalent circuit of the electrode elements of Fig. 2.

and R2 fa Referring to the drawings, l designates the core of the cathode of an electric discharge tube, it being possible for said cathode to be heated either directly or indirectly, as by a heater l-h, 2 designates the emitting layer of the cathode and 3 the next following electrode, depending upon whether the discharge tube is a triode or a diodejt being shown here for example as a triode and having an anode 4, and an enclosing glass envelope 5, which may be a grid or the anode. If the tube has to be suited to the use on a wavelength of 50 centimetres and Q0 is equal to 100, whereas R0 is 500 ohm-ems, it is seen that the value d/a hereinbefore mentioned must be equal to or less than 0.06, that is to say at a distance of microns of the external surface of the emitting layer 2 from the electrode 3, as is a normal distance for tubes suitable for generat ing or amplifying very short waves, the thickness of the emitting layer 2 cannot be in excess of 6 microns.

What we claim is:

1. An electric discharge tube for amplifying or generating electric oscillations of very high frequencies, comprising a cathode having a supporting base and a layer of electron-emitting material thereon, and an adjacent electrode closely spaced therefrom, the distance of the emitting layer of the cathode. from the said adjacent electrode being less than 0.5 mm. and the ratio of the thickness of this layer to the distance just mentioned is less than 0.10.

2. An electric discharge tube as claimed in claim 1, wherein the thickness of the emitting layer of the cathode is less than 25 microns.

3. An electric discharge tube as claimed in claim 1, wherein the thickness of the emitting layer is less than 10 microns.

4. An electric discharge tube as in claim 1, wherein the distancev of the external surface of the emitting layer from the said adjacent electrode is less than 0.1 mm. 7

MAXIMILIAAN JULIUS OTTO S'I'RUTT. ALDERT VAN .DER ZIEL.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS 1 Number Country Date 115,700 Great Britain May 21, 1918 Certificate of Correction Patent No. 2,478,986 August 16, 1949 MAXIMILIAAN JULIUS OTTO STRUTT ET AL. It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 4, line 10, after the numeral 5 strike out the comma; same column,

line 6, beginning with the comma and word depending strike out all to and including envelope 5 in line 10, and insert the same in line 11, after the syllable ode and before the period; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 27th day of December, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

